The invention relates to an optical branching device. The device comprises two polarization-sensitive beam splitters for forming and combining two linearly polarized radiation beams having mutually perpendicular polarization directions. Arranged between the polarization-sensitive beam splitters, the branching device comprises an optical device for rotating the plane of polarization of the parallelly propagating beams. The polarization-sensitive beam splitters each comprise two components which have adjoining plane surfaces, one of which is the base of a prism.
Such an optical branching device has been proposed for use as an optical circulator by H. Iwamura and Y. Suemune in an article entitled "Optical Isolator and Circulator Using Y.sub.3 Fe.sub.5 O.sub.12 Crystals for Optical Fiber Transmission Systems" (FERRITES: Proc. of the Int. Conf., September-October 1980, Japan, pages 787-790). The polarization-sensitive beam splitters each comprise two calcite prisms whose bases are placed against each other. In addition, each beam splitter has an associated optical deflection element, for example a deviating prism. The deviating prism ensures that the two linearly polarized beams propagate in parallel directions and that these beams traverse the optical polarization rotating device arranged between the two beam splitters. The optical polarization rotating device comprises a Faraday rotator and a half-wave plate.
A similar optical branching device used as an optical switch is disclosed in, for example, German Offenlegungsschrift 3,241,894 (corresponding to U.S. Pat. No. 4,410,238). The optical device arranged between the polarization-sensitive beam splitters with deflection elements now comprises a liquid crystal layer between two electrodes. The electrodes form an electric field inside the liquid crystal layer.
Both optical branching devices have the disadvantage that their polarization-sensitive beam splitters each comprise two prisms consisting of birefringent mono-crystals. Such prisms are comparatively expensive and are therefore not suitable for general use in optical data or communication systems.
Another disadvantage is that each polarization-sensitive beam splitter must be used in conjunction with an optical light deflection element, for example a mirror or a deviating prism. This results in larger optical branching devices, so that these devices are not suitable for use in integrated optical fiber systems.